1. Field of the Invention
This invention relates generally to gas turbine engines and, more particularly, to an apparatus for detecting and indicating the occurrence of a gas turbine engine stall.
2. Description of the Prior Art
As is well known in the art, during the operation of an aircraft gas turbine engine there may occur a phenomenon referred to as stall, wherein a momentary reversing of the airflow occurs through the compressor. This causes the compressor discharge pressure to decay very rapidly, and occasionally results in pressure oscillations through the compressor until corrective action is taken. A stall may result from a variety of reasons such as an engine acceleration which is too rapid, an unduly distorted inlet air temperature or pressure profile, or compressor damage due to the ingestion of foreign objects or malfunctions. The principal cause of stall is aerodynamic overloading of the compressor for the particular rotational speed and inlet temperature at which the engine is operating.
Prior art devices have attempted to sense when a stall was imminent and either warn the engine operator to take corrective action or, as is described in U.S. Pat. No. 3,852,958, assigned to the assignee of the present invention, automatically take corrective action to prevent the occurrence of a stall or to minimize its effects. While these prior art devices have achieved a certain amount of success in avoiding and/or compensating for the effects of a stall they generally are comprised of complex electronic or electrohydraulic components which add unnecessary weight and expense to the engine.
An alternate approach is to design the engine control system so as to avoid the area of engine operation where a stall is likely to occur. Although this approach has been highly successful in avoiding stalls, there are still some occasions where a stall may result. For example, there may be an undetected transient malfunction in the engine control system which may allow a stall in certain circumstances.
The present invention provides an apparatus for detecting and indicating the occurrence of a stall so that corrective action, for example correcting an undetected transient control system malfunction, may be taken.